1. Field of the Invention
The invention relates to an electric machine having a hollow rotor shaft and a device for cooling the rotor shaft.
2. Description of the Related Art
EP 0 660 492 A1 discloses an electric machine with a rotor shaft that is cooled by transmission oil of a transmission. The transmission has an input gearwheel connected fixedly to the rotor shaft so as to rotate with it. Transmission oil is guided from a gearbox into the rotor shaft as coolant and is returned from the rotor shaft back into the gearbox.
The cooling of the rotor shaft of EP 0 660 492 A1 disadvantageously is dependent on the volumetric flow and on the temperature of the transmission oil and the transmission oil heats up during the passage through the rotor shaft. Furthermore, special seals are needed in the region of the rotor shaft that guides the transmission oil.
It is an object of the invention to provide an electric machine with a hollow rotor shaft that achieves optimum cooling of the rotor shaft and optimum oil routing in the region of the rotor shaft, without substantial heating of the oil.